I have not had much luck with dwarf cichlids at all really. I had heard that this Laetacara species is overall more peaceful than other cichlids, which I initially found out to be true. It was quite an attractive centre piece fish. But now that I have had a whole group of 20 cardinal tetras almost totally wiped out in a similar way (Died off one by one, no obvious injuries other than on a few individuals or disease symptoms but this was when I had Apistogramma that I rehomed after the incident), as well as seeing this cherry barb with these sort of injuries, I'm wondering if I should possibly reconsider this stocking plan and try to rehome the Laetacara. The survivors of the (highly likely) Apistogramma incident had also been possibly picked off by this fish while the tank was under the care of a "fish sitter" by the same male. Absolutely demotivating. I guess it's sort of my fault being ignorant about this sort of outcome being a realistic possibility. I had imagined they'd be able to get away and not be bothered by the Laetacara as I had researched a decent amount about them and come to the conclusion they would be a good cichlid to have with some smaller, peaceful fish. I am keeping the fact that it could be water quality issues or some mystery disease in mind, and I'll have to probably wait and see one get attacked before I can assume this male is killing any fish.
I also want to keep in mind water quality issues are very possibly a contributing factor. I had actually stopped using tap water after the mass cardinal tetra die off (R/O is a more reliable source) and after the Laetacara female had died. My Laetacara male has been doing great for over a year now along with a small group of cherry shrimp, but I do think cherry shrimp could honestly live in a toilet. I also think if there was a water quality issue the Laetacara would surely appear stressed or not be doing so well, and that the fish would obviously appear stressed or sick before dying. But I can't really know that for sure. I mix my own R/O and change 25 percent of the water around 2 or 3 times a week, or do 50 percent once a week.